(1) Field of the Invention
The present invention relates to a method of evaluating whiteness of light from a light source, a method of evaluating comparative whiteness, a light source and a luminaire that produce light with whiteness evaluated as being high by the method of evaluating whiteness.
(2) Related Art
Development of light sources and luminaries has conventionally been directed toward reproducing the original colors of an object to be illuminated faithfully. Specifically, luminaire that can provide color appearance of an object closer to that provided under a standard illuminant have achieved a high reputation. This can be objectively evaluated using the general color rendering index.
In recent years, however, desirable color appearance has been drawing attention instead of fidelity of color appearance. As a result, techniques for developing light sources and luminaries to render light colors as desired for specific applications are receiving attention. Some lamps have already been developed, such as those for making foods placed on the shelf look good or making plants at flower stores look more beautiful. To evaluate the desirable color appearance, visual clarity index is proposed in Japanese Laid-Open patent application No. 9-120797, which indicates how vivid an object color is rendered.
It is pointed out that light colors affect our perception of brightness (See Urabe et al., “Color Temperature of Light Source for Interior Lighting . . . The Effects on Brightness, (1) Impression from outside by Method of Paired Comparisons”, Annual Conference of The Illuminating Engineering Institute of Japan, 1995.). In other words, the whiter a white object is rendered, the brighter the object appears to the human eyes. Also, as the feeling of whiteness increases, the Figure of an object looks neat. This would help make the visual environment more comfortable. Accordingly, it is desirable to use a luminaire with high whiteness while maintaining the vividity of color appearance.
However, evaluation measurements of such whiteness have conventionally relied on subjective judgments. For the same reasons, users have found it difficult to choose lighting devices.